Apparatus and method for spinal fixation and correction of spinal deformities

ABSTRACT

This device comprises an connection element (4) between a rod (1), or other longitudinal implant, and a bone anchorage screw (3) in the degenerative vertebra. This connection element (4) includes a ring (8) so dimensioned that the rod (1) is capable of extending therethrough. The ring is provided with screws (14) for clamping to the rod (1) and is radially extended by a cylindrical arm (9) adapted to be secured to the bone anchorage screw (3) and to be clamped on the screw. The arm (9) and the ring (8) constitute a unit in one piece. The invention enables the surgeon to avoid having to produce additional deformations of the rod (1) when it is in presence of non-aligned pedicles by leaving to the surgeon complete liberty as to the position of the two axes of the bone anchorage screw (3) and of the rod (1). The invention further contemplates using the lateral connection element to facilitate contouring the longitudinal implant within the patient, or in situ to segmentally and globally correct spinal deformities in all degrees of freedom.

This application is a 35 U.S.C. 371 application of PCT/US95/09919, filedOct. 15, 1993.

BACKGROUND OF THE INVENTION

The present invention concerns an apparatus for spinal osteosynthesis,applicable notably to degenerative or misaligned vertebrae.

It is known that the vertebrae, in particular the lumbar vertebrae, aresubjected to a concentration of stresses, in which the discs and theligaments play a significant compensating part. If these vertebraebelong to a relatively aged body, they undergo a certain degeneration,which makes the discs and the ligaments unable to completely fulfilltheir role by reason of their aging.

These vertebrae then, are subjected to a certain instability and tend todisplace relative to adjacent vertebrae. These displacements areuncontrolled and can be: displacements in angularion and rotation,medio-lateral and antero-posterior displacements, or else thecombination of these displacements.

It is therefore necessary to remedy this situation, which risksgenerating a compression or compromise of the spinal cord of thepatient, by endeavoring to put the displaced or misaligned vertebraeback to their positions.

SUMMARY OF THE INVENTION

The spinal osteosynthesis device, according to the invention, comprisesat least one longitudinal implant, such as a rod, and by preference two,together with bone anchorage elements joined to the rod, such as screwsor hooks.

In accordance with the invention, this device comprises at least oneconnection element between the rod and a vertebra to be treated, andmeans for fixation of this element to the vertebra, this elementincluding a body, such as a ring or collar, so dimensioned that the rodcan be mounted therein to move freely in rotation and in translation onthe rod and outfitted with means for fixing the ring on the rod andextended radially by an arm, this arm and the ring forming a one-pieceunit.

In this way the terminal ring of the connection element can be mountedto be trapped on the osteosynthesis rod or longitudinal implant, whilebeing still free in translation and in rotation before its fixation inthe chosen position on the osteosynthesis rod, by way of a suitablemeans for fixing.

According to one aspect of the invention, the means for fixation of theconnection element to the vertebra to be treated is advantageously abone anchorage element, such as a screw or a hook of a known type, andwhose body is open in a U-shape in order to permit introduction into itof the free end of the arm of the connection element. The inventioncontemplates that the anchorage element be free to both translatemedio-laterally along and rotate/angulate around the extended radial armof the connection element. This aspect of the invention can beimplemented with a hook having a closed body with the longitudinalimplant or rod extending through an opening in the hook body.

In another aspect of the invention, the aforementioned lateralconnection element is used in a novel method for correction of a spinaldeformity. This method provides for correction segmentally along theentire length of the spine, in all three degrees of freedom and alongthe three columns (posterior, middle and anterior) of the spine. Thismethod contemplates implanting a strong yet ductile longitudinal implantbetween several vertebrae. In one embodiment, the implant is anosteosynthesis rod, although this method can be applied using a bar orplate. The vertebrae are instrumented with fixation elements, such ashooks or screws, and the fixation elements are engaged to thelongitudinal implant, or rod, in a manner that permits free slidingtranslation and rotation of the fixation elements with respect to therod. In the preferred embodiments, this engagement is effected by thelateral connection element.

Once the instrumentation is in position, the spinal rod is contouredwithin the patient, or in situ, until the rod has assumed the shape of aproperly oriented spine. As the rod is contoured in situ, the fixationelements engaged to the vertebrae impart corrective forces to thesuccessive motion segments. Since the fixation elements are free totranslate and rotate relative to the rod-being contoured, the motionsegments are allowed to automatically and naturally seek their properanatomic position. This in situ contouring approach involvesmanipulation of the motion segments so that the axes of movement of thesegments is as near to the neuroforamina as possible to avoid the riskof compromising the neural canal.

An important feature of the invention that permits application of the insitu contouring approach is the material properties of the longitudinalimplant. The implant must naturally be strong enough to withstand theoften severe loads imposed on it by the spine. The implant must also bestiff enough to resist deformation under these loads once theinstrumentation is complete. At the same time, the implant must beformed of a material that is sufficiently ductile to allow the implantto be deformed within the patient and substantially retain that imposeddeformation. Given the narrow confines in the spinal region, it isundesirable to "over contour" the implant with the expectation that the"springback" properties of the implant will decrease the finaldeformation. Thus, the implant material preferably exhibits an optimumductility, or more particularly, maintains in its final position a highpercentage of the imposed deformation.

In order to achieve this novel in situ contouring and correction,specially designed tools are provided. One tool, a traction rotator, isconfigured to engage the ends of a lateral connection element so as toprovide a rotational force to the element. In addition, the tractionrotator can have forked arms at its end to contact a body engaged to thearm of the lateral connection element to apply a traction force to thatbody. A second tool, a counter-rotator, is configured to engage thelateral connection element at a lower vertebral level to hold this lowerelement fixed while a subsequent level is operated on by the tractionrotator.

Bending irons are set forth in a further aspect of the invention whichare specially suited for manifesting this in situ contouring approach. Aright angle or L-bender permits bending the rod within the patient inthe sagittal plane. A rod grip bender provides a cylindrical surface forgripping the rod as it is bent. This rod grip bender greatly reduces thelocal deformation experienced by the rod as the bending force istransmitted through the bender to the rod.

The present invention contemplates instrumentation over several lumbararid thoracic vertebral levels. In addition, another feature of theinvention resides in intrasacral fixation at the distal end of thelongitudinal implant. In accordance with one embodiment, thelongitudinal implant, such as a rod, is extended into a bore formedinferiorly from the L5-S1 junction. A sacral screw having an obliquecanal for receiving the rod is buried into the lateral sacral mass,generally beneath the iliac crest. The iliac crest provides a"buttressing" effect to resist pullout of the sacral screw and to helpalleviate the loads exerted on the screw and rod at the L5-S1 junctionby pelvic rotation and bending. This "iliac buttress" combines with theproximal sacral screw and the distal rod engagement within the sacrum toform a firm and strong foundation for the longitudinal spinalinstrumentation.

In yet another aspect of the invention, the lateral connection elementcan be used to position a plurality of vertebral fixation elements at asingle level. In one embodiment, one lateral connection element isengaged to a spinal rod, while another lateral connection element isengaged to the first. On vertebral fixation element is engaged to therod, while a second fixation element is engaged to the second lateralconnection element, which can extend substantially parallel to theprincipal rod. In this manner, the first and second fixation elementscan be oriented laterally virtually side-by-side. For example, a pediclehook and a supralaminar hook can be situated at the same level. Inanother embodiment, a laminar hook can be associated with a vertebralfixation screw, so that the hook can strengthen the construct againstscrew pullout.

It is one object of the present invention to provide a spinal fixationsystem for the correction of spinal deformities that accommodatesmultiple, and even variable, positions of a vertebral fixation elementrelative to a longitudinal implant. Another object resides in a methodfor correcting the spinal deformity that can be implemented withfixation elements engaged at any one of many positions in the vertebrae.

Some other details and benefits of the inventions will appear in thecourse of the description which follows, taken in reference to theannexed drawings which illustrate one preferred embodiment by virtue ofnon-limiting examples.

DESCRIPTION OF THE FIGURES

FIG. 1 is a view in exploded partial perspective of one preferredembodiment of a spinal ostheosynthesis device including connectionelement according to the invention used between an osteosynthesis rodand a bone anchorage screw.

FIG. 2 is a view from above in enlarged scale of the connection elementdepicted in the FIG. 1.

FIG. 3 is a view in perspective of a spinal osteosynthesisinstrumentation embodying one device according to the invention, set inposition on a spinal section in which one of the vertebrae is displacedto be returned into alignment with the others.

FIG. 4 is an analogous view to FIG. 3 showing a bone anchorage screw andthe corresponding vertebra in the course of translation on the arm ofthe connection element according to the invention.

FIG. 5 is an analogous view of FIG. 4 showing the vertebra and theassociated pedicle screw in their definitive position, at the end ofsliding on the arm of the connection element and after rotation of thering on the principal rod.

FIGS. 6A-c are side schematic representations of a spinal motion segmentdepicted in the sagittal plane and showing the location of the axis ofthe segment during normal movement of the spine.

FIGS. 7A-B are schematic representations of a motion segment viewedposteriorly in the frontal plane and showing the location of the axis ofthe segment as the spine moves.

FIGS. 8A-B are schematic representations of a motion segment viewedinferiorly in the transverse plane and showing the location of the axisof the segment as the spine moves.

FIGS. 9A-C are schematic representations of a motion segment viewed inthe sagittal plane in which the segment is instrumented with alongitudinal implant that is contoured in situ in accordance with theprinciples of the present invention.

FIG. 10 is a graph of ductility for the material of the longitudinalimplant used in the in situ contouring technique. 5 FIGS. 11A-B areperspective views of a spinal segment in which one vertebra is displacedand then subsequently manipulated into its proper anatomic position.

FIGS. 12A-B are top and side elevational views of an L-bender for use inin situ contouring of a longitudinal implant.

FIGS. 13A-B are side and top elevational views of an rod grip bender foruse in situ contouring of a longitudinal implant.

FIGS. 14A-B are top and side elevational views of a traction rotatortool for use in direct derotation of spinal instrumentation inaccordance with the present invention.

FIGS. 15A-B are side and top elevational views of a counter-rotator toolfor use in direct derotation of spinal instrumentation.

FIG. 16 is a top elevational view of a lateral connection elementmodified for use with the tools shown in FIGS. 14-15.

FIGS. 17A-B are anterior views in the frontal plane of three vertebraein which one displaced vertebra is restored to its proper anatomicposition by direct derotation.

FIGS. 18A-B show in the sagittal plane the direct derotation depicted inFIGS. 17A-B.

FIGS. 19A-B show in the transverse plane the direct derotation depictedin FIGS. 17-18.

FIGS. 20A-B are side elevational and top perspective views showing thesacral fixation techniques and "iliac buttress" of the presentinvention.

FIGS. 21A-B are side and top elevational views of spinal instrumentationusing the multiple lateral connection elements to permit multiple singlelevel instrumentation of a vertebra.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

One sees in FIGS. 1 and 2 an osteosynthesis rod 1 of which the surfacepresents a multiplicity of asperities 2, for example forming the pointsof a diamond, a bone anchorage pedicle screw 3 and a connection element4 between the rod 1 and the screw 3 positioned laterally or medially tothe rod 1 in a pedicle.

The pedicle screw 3 is constituted by an open and U-shaped body 5 and bya threaded section 6, which is of the type of the one described in theFrench patent 89 04 925 (2 45 732) in the name of Yves Cotrel. The screwis normally adapted to receive, between the branches 5a of body 5, a rod1 with asperities. Threaded apertures 7 are defined in the branches 5ato receive screws 19 (FIGS. 4-5) provided for fixing on the rod, thisfixation being completed by a cylindrical clamping member 17 closingchannel 10 of body 5.

Clamping member 17 is so dimensioned to be introduced in the U-shapedbody 5 with arm 9 extending therethrough. It includes a central screw 18capable of being screwed into a threaded aperture in a radial boss 23dimensioned to slide between the ends of the branches 5a. Clampingmember 17 is moreover pierced by apertures 22 for passage of the lateralscrews 19, and is provided with a collar 24 forming a shoulder adaptedfor support on a corresponding face 25 defined on an entrance edge ofchannel 10 of body 5.

The element 4 includes a body, such as ring 8, dimensioned to be able toreceive principal rod 1 extended therethrough, and an arm 9, preferablycylindrical and of a diameter substantially equal to the one of thechannel 10, extending radially from ring 8 to a suitable length, andforming a one-piece unit with the ring. The arm 9 is adapted to be ableto penetrate and Slide in cylindrical channel 10. Its surface preferablypresents a multiplicity of asperities 11 (FIG. 2), Which could besimilar to asperities 2 on rod 1. The surface of the arm with asperities11 is joined to ring 8 by a smooth section 12 of diameter slightlysmaller than the one of the portion with asperities.

Apertures 13, numbering four in the represented example (although othernumbers are possible), are radially disposed in ring 8, so that one pairof apertures is symmetrical to the other pair with respect to diameterXX of ring 8, which intersects the axis of arm 9. These apertures 13 canreceive corresponding screws 14 for clamping the element 4 againsttranslation and rotation on rod 1 in the chosen position. The solidityof this fixation is increased by asperities 2 which afford a connectionof very high mechanical quality.

Pedicle screw 3 constitutes a means of fixation of arm 9 of element 4 inthe degenerative vertebra to be treated. In order to do this, arm 9 isintroduced in U-shaped body 5 and blocked by the aforementioned means 7,17, 18 and 19. Clamping member 17 closes the aperture of the U in body 5assuring the security of the mounting. Indeed, in the event of thebreakage of lateral screw 19, arm 9 cannot, due to the fixing of member17, become detached from the body 5 of the screw 3.

The ring 8 can be mounted free in translation and in rotation on theprincipal rod 1 and can then be locked on the rod by the radial meansconstituted by screws 14.

Alternatively, the means for fixation of arm 9 on the vertebra to betreated can be formed by a threaded plug, according with the teaching ofthe French patent 2,633,177 (88 08538) or by a system similar to thatdisclosed in the French patent 2,545,350 (83 07450). The asperities onarm the 9 and on the rod 1 are preferably formed, but not necessarily,according to the French patent 2,545,350 (83.07450). (These asperitiesconstitute the means for anchorage of the extremities of screws 14, 18and 19.)

The osteosynthesis instrumentation illustrated in FIGS. 3 to 5 includestwo straight rods 1, 1A extending the length of three vertebrae, forexample L3, L2, L1, and joined by known transverse connection devices21. (These devices 21 and the rod 1A are represented in phantom in FIG.5.) The intermediate vertebra L2 is shifted with relationship to theothers and must therefore be restored to its desired position bypositioning the instrumentation.

The osteosynthesis device according to the invention is placed inposition by the surgeon in the following manner.

The osteosynthesis rods 1 and 1A are firmly set in two points ofanchorage to vertebrae adjacent lumbar vertebra L2. The two anchoragepoints of rod 1 are then accomplished on the adjacent vertebrae L1 andL3, by screws such as 15 (FIG. 3), of a known type. The surgeoncompletes the mounting with the transverse connection devices 21jointing rods 1 and 1A (FIG. 5).

The rod is intended to serve as the support for lateral connectionelement 4, which is previously loosely joined to it by axialintroduction of ring 8 on rod 1. The ring 8 becomes trapped but is freein rotation and in translation, in the free space separating fixationscrews 15 from osteosynthesis rod 1.

The means for fixation of element 4 to the degenerative vertebra L2 tobe treated, for example a pedicle screw 3, is fixed to this vertebra L2.The free end of arm 9 can then be easily introduced in channel 10 ofU-shaped body 5, and can stay free in translation and rotation. Theaction of the surgeon consists then, with the assistance of suitabletools, to reposition the vertebra L2 with relationship to the adjacentvertebrae L1 and L3, to its original position. To do this, the surgeonmanipulates body 5 of the screw 3. This having been done, the rotationalposition of ring 8 in relationship to osteosynthesis rod 1 isautomatically modified, and in this way too the position of body 5 ofthe pedicular screw 3 along the length of the lateral connection arm 9.

As soon as the surgeon decides that the given vertebra L2 is in thedesired position with relationship to the adjacent vertebrae L1 and L3,the surgeon tightens the connections by first the anchorage screws 14,on rod 1, then screws 18, 19 on arm 9, in order to achieve:

on one hand the fixation in rotation of ring 8 on the osteosynthesis rod1

on the other hand, the fixation in translation and rotation of body 5 ofscrew 3 on lateral arm 9.

The position of the vertebra L2 to be treated is then firmly maintainedmechanically by instrumentation. Of course the second osteosynthesis rod1A of the instrumentation does not need to be likewise provided with alateral connection element 4.

The presence of asperities on the whole surface of the rod 1 and the arm9 allows a quality anchorage of the blockage screws 14, 18 and 19 to beobtained on all points of displacement. These screws act radially on rod1 and arm 9 by exerting a strong pressure, thereby assuring a favorableconnection in rotation and translation.

Connection element 4 according to the invention enables the surgeon tolink a rod 1 of an osteosynthesis instrumentation of theCOTREL-DUBOUSSET type to a pedicle screw or to a sacral screw, leavingit with complete freedom in the respective position of the tworespective axes of the rod and screw (angles and distance). Indeed thissystem permits a rotation of the vertebra in the horizontal ortransverse plane, while letting this vertebra place itself angularly inthe sagittal plane without incurring interference constraints, thanks tothe degrees of freedom allowed by the mounting. Using two connectionelements together provides even greater degrees of freedom by themountings.

The invention is not limited to the preferred embodiment described, andcan include several variants of its implementation.

Thus, instead of being completely closed as represented in the drawing,the ring can be opened or presenting a slot 20 (FIG. 1). The blockage orfixation element such as screws 14 (the number of which can evidentlyvary while being at least one), then extend through the ring on eachside of slot 20. Likewise, anchorage screw 3 can be substituted by ascrew similar to the one represented in FIG. 4 of French patent2,645,732 (89 04 926), having lateral branches of unequal lengths whichdefine a lateral aperture, and no longer a rear opening, for theintroduction of arm 9. Clamping member 17 is them obviously modified toaccommodate this asymmetrical body. This last type of screw brings asupplementary security in the maintenance of arm 9. Clamping member 17can likewise be replaced by one of the fixing elements described inFrench patent 2,645,732.

The pedicle screw linked to the degenerative vertebra can likewise be aclosed head screw. It can also be replaced by a spinal hook providedwith a channel for receiving connection element 4. This channel couldbe, like the screw, closed or else upwardly open, and presenting asimilar U-shape. The U-shaped head of the hook or the screw, could beclosed by a threaded plug such as described in French patent 2,633,177(88 08 538) of 24 June 1988 filed by Yves Cotrel.

Finally, apertures 13 defined in ring 8 can be in number more or lessthan those described previously in the preferred embodiment.Advantageously, they can be arranged on the ring so that, whatever therotation of ring 8 on rod 2 is during the repositioning of thedegenerative vertebra by the surgeon, one or several apertures areeasily accessible to introduce there a clamping screw on rod 2.

As thus far described, the novel connection element 4 provides means forvarying the orientation of the fixation screw, such as screw 5, relativeto the primary rod, or rod 1. As explained above, manipulation of thedisplaced vertebra causes the connection element 4 to rotate and itsengagement with the screw 5 to translate along the length of the arm 9until the vertebra is in its proper position. At that time, the severalclamping screws can be tightened to form a rigid construct.

The connection element 4 has been found to be important in anothermethod for fixation of the spine and correction of spinal deformities.In this alternative method, rather than manipulating the vertebra itselfinto position, the instrumentation is manipulated to adjust the positionof the displaced vertebra. In this instance, then, the fixation oranchorage element 3 translates a corrective force to the vertebra,rather than as in the previously described method in which the vertebratransmits a displacement force to the components of the connectionelement.

In order to facilitate an understanding of this novel method, it isfirst valuable to understand the biomechanics of the spine and itsmotion segments, as developed by the present inventor. The term "motionsegment" as used herein constitutes adjacent vertebrae and the disctherebetween. First with reference to FIG. 6A, it can be seen that thespine can be divided into three columns along its length--the anterior,middle and posterior columns. The inventor has found that correction ofspinal deformities requires consideration of correction in each of thesethree columns.

Prior art techniques for correcting spinal deformities have tended tofocus simply upon one of the three columns, usually the posteriorcolumn. For example, the original Harrington system contemplatedcompression or distraction using posterior instrumentation. Thus, theHarrington instrumentation achieves compression or distraction of theposterior column of the spine, without specific consideration of theimpact to the spine in the remaining two columns. In subsequentsegmental systems that implement anchorage elements at each vertebrallevel, again the corrective forces are applied typically in but a singleone of the columns, which may lead to difficulties in the other of thecolumns of the spine.

In other systems, the spine is translated to a rigid rod. Examples ofthis approach can be found in the Luque Wiring System, sold by DanekMedical, Inc., and the Isola System of AcroMed Corp. These systemsprovide little control of transverse rotation of the motion segments. Athird approach involves engaging a pre-contoured rod to the spine andthen rolling the rod to thereby alleviate an abnormal scolioticcurvature. This approach again provided little control over transverserotation.

Understanding of this new method also requires consideration of thespinal motion segments, or the the relative movement between twoadjacent vertebrae and their connecting disk. Proper correction ofspinal deformities requires consideration of the biomechanics of themotion segment at each level and particularly requires awareness of howthe axes of motion of the segment moves as the segment is subjected tobending, tilting, angularion and rotation. As will be more apparent fromFIGS. 6, 7, 8, the axes of the motion segments both rotate andtranslate. Failure to consider both types of motion may yield inferiorcorrection and may lead to other complications. Accommodating therotation and translation of the motion segment axes is important topermit separate control of each of the three columns of the spine aswell as correction in each of the three planes.

Prior approaches do not account for the complicated biomechanics of thespine. Distraction or compression in prior rod systems utilizingpre-contoured rods tend to place the angle of angularion of the spinalsegment far removed from the true axis of the motion segment. Typically,this axis of angulation in prior systems is in the pedicle into whichtime screw is inserted and not at the level of the disc, deformity orinjury. As can be seen from the following discussion, this approach iscontrary to the normal biomechanics of the spine.

Referring first to FIGS. 6A-6C, a spinal motion segment is depicted inthe sagittal plane. In FIG. 6A, the neutral position of the motionsegment is shown in which the axis A is located in the middle column andposteriorly and inferiorly in the disk. In the sagittal plane, themotion segment is subject to angulation in which the adjacent vertebraerotate relative to each other. In the case of flexion, as shown in FIG.6B, the axis A moves anteriorly and superiorly into the center of thedisk. On the other hand, in extension, as shown in FIG. 6C, the axismoves posteriorly and inferiorly slightly below the inferior endplate ofthe disk. It is thus apparent that the axis of each spinal motionsegment translates with angulation in the sagittal plane.

The same phenomenon is exhibited in the frontal plane, as shown in FIGS.7A and 7B. In FIG. 7A, the neutral position of the axis A is along themidline of the spine and somewhat below the center of the disk close tothe inferior endplate. With the inferior vertebra held stationary, thesuperior vertebra can bend laterally, or tilt, to the right or to theleft. A tilt to the right is depicted in FIG. 7B, in which it is seenthat the axis A moves not only laterally to the left but also somewhatcephalad into the disk. A tilt to the left would product an oppositelateral movement of the axis with a similar cephalad movement. Again,the axis of the motion segment translates in the frontal plane.

Finally, the vertebrae appear in the transverse plane in FIGS. 8A and8B. In the neutral position shown in FIG. 8A, the axis A is disposedgenerally in the centroid of the neural canal C. With rotation to theright or left, the axis A always remains within the neural canal, asshown in FIG. 8B for rotation to the right. The axis does shiftlaterally somewhat in a direction opposite to the rotation, butnevertheless always remains within the canal. This is an importantaspect of proper motion of a spinal motion segment since maintaining theaxis of the motion segment within the neural canal is protective of allof the neural elements passing therethrough. It is believed that manyprior systems and techniques for correction of spinal deformities have atendency to displace the axis out of the canal leading to an increasedrisk of damage to the neural elements. It can be seen from this view inthe transverse plane that the vertebral motion segment has a very narrowwindow of movement before the axis of the segment leaves the canal C.Any correction applied to the spine that does not take into account theaspects of rotation in the transverse plane of a motion segment carriesthe risk of damaging the neural elements housed within the canal.

From the foregoing FIGS. 6-8, it can be seen that every segmental spinalmotion segment involves both translation and rotation in each of thethree planes (sagittal, frontal and transverse). Thus, in the frontalplane, the motion segment can translate up and down and left to right,and can rotate or tilt left or right. In the sagittal plane, the segmentcan translate up and down and posteriorly and anteriorly, while it canrotate, or more particularly angulate, in flexion or extension. Finally,in the transverse plane, the motion segment biomechanics yieldstranslation to the right or left, or anteriorly or posteriorly, androtation to either the right or left, again always maintaining the axiswithin the neural canal.

With this explanation of the movement of the spinal motion segments, itcan be appreciated that optimum correction of spinal deformities shouldpermit the motion segments to move in the manner for which they weredesigned. In relation to the three spinal columns discussed above, it isalso important to control the correction of the deformity by keeping themotion segment axes between the longitudinal implant, or rod, and themiddle spinal column, or close to the neural canal. With the presenttechnique, it is possible to achieve elongation or distraction of theanterior and middle columns anterior to the motion segment axis, andapproximation or compression of the posterior column behind the axis. Inaccordance with the present invention, the surgeon, and not theinstrumentation, determines the location of the motion segment axes.

A further feature of the invention provides the means for achieving thisoptimum segmental and global correction of the spine. More particularly,the invention contemplates in situ contouring of a longitudinal spinalimplant when it is engaged to several vertebral bodies by screws orhooks. While the longitudinal implant may be a plate or bar, the presentembodiment contemplates the use of a spinal rod, such as previouslydescribed. Contouring the rod alone is not sufficient and will frustratethe normal movement of the three columns of the spine and the spinalmotion segments. Specifically, in situ contouring of a rod rigidlyengaged to the spine will simply translate the vertebrae withoutconsidering the needs of the motion segment axes explained previously.

Thus, a further aspect resides in connecting the vertebral fixationelements, such as bone screw 3, to the rod, such as rod 1, in a mannerthat permits free rotation and translation of the vertebra to which thebone screw is attached relative to the rod as it is being contoured.This capability is achieved by the collar or ring 8 engaged to the rod1, as well as the cylindrical fixing element 17 engaged to the arm 9 ofthe ring 8. As previously described, each of these components is free totranslate and rotate relative to the component to which they areengaged. In this manner, as the rod is contoured, corrective forces areapplied to the vertebral segment while the free degrees of rotation andtranslation permit the vertebra to seek its proper biomechanicalorientation. In addition, this approach accommodates the needed andnecessary translational and rotational degrees of freedom in each of thethree planes of a spinal motion segment.

This inventive approach to instrumentation of the spine and correctionof spinal deformities can be readily understood from a few diagrammaticrepresentations. Referring first to the examples in FIGS. 9A-9C, in situcontouring of the rod in the sagittal plane is depicted. It isunderstood that the system can be generally constructed as illustratedin FIG. 3, such as by implementing a rod 1 engaged to the vertebrae byway of a bone screw assembly 15. The construct in FIG. 9A represents theuncorrected position of a spinal motion segment. In this position, thebone screw assemblies 15 are displaced from each other by a distance d₁.In this arrangement, the axis A of the motion segment is located in themiddle of the disk D, similar to the position illustrated in FIG. 6B. Inorder to restore the segment to its proper position or alignment, and inorder to exert a proper and precise biomechanical force for thiscorrection, it is necessary that the axis P along which the correctiveforce is applied be able to translate in the anterior/posteriordirection.

This neutral position is shown in FIG. 9B which shows the spinal motionsegment after application of a bending force to the rod 1. This bendingforce is applied between the two bone screw assemblies 15 so that therod 1 is essentially bent around pivot point P, with the ends of the rodmoving in the direction of the arrows 30. In order that the axis A bepermitted to translate, it is necessary that the bone screw assemblies15 be able to slide along the rod 1 in the direction indicated by thearrows 31. Permitting this free translation of the screw assemblies 15along the rod 1 allows the anterior disk space to open or elongate inthe direction of the arrows 32. Some compression of the posterior diskspace may also occur. In this instance, contouring the rod 1 whilepermitting sliding movement of the screw assemblies 15 leads to adecrease in the distance between the screws, as represented by thedistance d₂, which is less than their original uncorrected distance d₁.It can further be seen that the axis A is now situated in its properneutral position as shown in earlier FIG. 6A.

The in situ contouring principles according to this invention alsocontemplate contouring the rod 1 with the screw assemblies 15 fixed tothe rod, as-shown in FIG. 9C. In this instance, the distance measuredalong the rod between the two screw assemblies 15 remains constant asdistance d₁. Contouring the rod 1 about the pivot point P not onlyproduces distraction at the anterior part of the disk, as represented byarrows 32, but also distraction at the posterior part of the disk asrepresented by arrows 33. This procedure may be important to open up thedisk space, such as to decompress the disk D.

It is also contemplated that both steps 9B and 9C can be implemented tonot only to control the axis A relative to its proper neutral position,but also to open up the neuroforamina as required. Therefore, the rod 1can be contoured slightly with the screws 15 free to translate along therod. Subsequently, the screw assemblies 15 can be fixed to the rod andfurther contouring of the rod 1 be accomplished to open up theneuroforamina. It is understood that with any spinal instrumentation, itis important that the neuroforamina remain open to avoid trauma to thespinal cord. In the preferred procedure to address this concern, thescrew assemblies are alternately locked and released on the rod, and therod contoured with each type of fixation to achieve an "averaged axis"in the sagittal plane with respect to the bending axis P. By this it ismeant that the axis P at which the contouring force is applied ismaintained as close to the neural canal as possible to avoid compromiseto the neuroforamina. Typically, the "averaged axis" will resideposterior to the disc and anterior to the longitudinal implant or rod.Under ideal circumstances, the longitudinal implant or rod would extendalong the length of the spine through the neural canal. Since this isnaturally not possible, the present in situ contouring principles allowthe "averaged axis" of the rod to be manipulated as close to theneuroforamina as possible.

With this example, many beneficial aspects of this inventive method canbe discerned. It should first be pointed out that this in situcontouring approach can be implemented with any longitudinal implant,such as rod, bar or plate. Optimum application of the in situ contouringtechnique requires that the osteosynthesis implant, such as rod 1, be astiff, strong and ductile one. This reference to a stiff strong ductheimplant encompasses many mechanical properties. It is important that theimplant be able to be bent without elastically springing back completelyor partially to its original position. Thus, while time rod 1 must beductile enough to be bent in situ, must be stiff or inelastic enough toavoid this "springback" effect. Finally, the rod 1 must be strong tosupport the biomechanical corrective forces being applied to thevertebrae. One rod-type longitudinal implant has been found thatfulfills each of these requirements, namely the Cotrel rod which formspart of the Compact Cotrel-Dubousset (CCD) system sold by SOFAMOR, S.A., of Rang du Fliers, France.

Other longitudinal implants can be acceptable, such as the Superflex rodsold by Danek Medical as part no. 808-088. The CCD rod, such as the CCD7 mm hyperquench rod, is formed of 316LVM low cold worked stainlesssteel. The preferred implant material has the strength of the low coldworked stainless with the requisite ductility. One measure of thisductility is the "springback" of the material, which can be expressed interms of the ratio between the residual and the imposed deformation ofan implant. This ratio is known to vary as the imposed deformationvaries, as reflected in the graph in FIG. 10. An optimum implantmaterial will exhibit a "springback" ratio of nearly ninety percent(90%) at imposed deformations of 20 mm or more.

It has been found that implants with higher "springback" ratio curves,i.e., that are more ductile, are better suited for the in situcontouring principles of the present invention, due, in part, to thelimited space available at the site of the instrumentation for"over-bending" the implant. It is, of course, preferred that the implantmaintain its imposed deformation, but it is understood that this"perfect" ductility arises at a sacrifice to strength. Theaforementioned spinal rod products exhibit the best known blend ofductility and strength for the in situ contouring procedure.

It should be appreciated that the illustrated in situ contouringtechnique, as enhanced by free sliding movement of the bone screwassemblies 15 relative to the rod 1, allows the spinal motion segmentfreedom of, movement in rotation and translation in each of the threeplanes of motion of the segment. This approach also permits optimumcorrection of the spine in each of the three spinal columns. With thisapproach, that is in situ contouring with the screw assemblies insertedthrough the pedicles into the anterior vertebral bodies, the screws areused as much for application of corrective forces as they are forultimate fixation of the system.

The method permits the greatest possible flexibility to the surgeon toadjust the location of the axis A of the vertebral motion segment simplyby selection of the manner in which the rod is bent and the fixityof-the screw assembly 15 to the rod 1. For instance, in the illustratedembodiment of FIG. 9B, rod benders are applied directly adjacent eachother at the pivot point P. Alternatively, the rod 1 can be bentimmediately adjacent a single screw, by placing the rod benders on bothsides and close to the head of the screw assembly, rather than betweenthe screw heads. In this instance, the specific screw will translate inthe sagittal plane but not angulate, and the particular vertebra willtranslate without rotation. The pivot point P can also be shifted towardone screw assembly or another to impart a differential angulationbetween adjacent vertebrae.

These in situ contouring principles can be applied for correction orcontouring anywhere along the spine. For instance, kyphotic contouringin the sagittal plane can be achieved by angulating or flexing thescrews in a motion segment and dorsally or posteriorly translating thesegment where needed. Lordotic contouring in the sagittal plane, used tocorrect kyphosis, can restore the segmental lordosis where neededwithout compression, thereby avoiding disk loading and closing of theneural foramen. Lordotic contouring with the screw assemblies 15unlocked and then locked on the rod can result in an "averaged axis" ofangularion situated between the back of the disk and the front of therod, that is somewhere within the spinal canal. Thus, this lordoticcontouring gives three column control with selective segmentalelongation of the spine anteriorly to the desired axis, and segmentalapproximation of the posterior column behind the axis. The segmentalapproximation of the posterior column is beneficial for posteriorfusion.

It can also be appreciated that this in situ contouring with freemovement of the fixation assembly on the rod, can correct tilt of agiven vertebra in the frontal plane (see FIGS. 7A-7B). In particular,the screw assemblies 15 are not only free to translate along the lengthof the rod but also free to rotate about the rod. As the rod 1 iscontoured in situ, the motion segment tends to seek its neutral axis inall three planes. Thus, a given vertebra may tend to tilt in the frontalplane, which movement is permitted because its fixation screw assembly15 is able to turn in the pedicle of the vertebra.

It has been found that translation of the spine in all three planesachieved by the in situ contouring principles is enhanced by use of thelateral connection element 4 previously described. To control torsion orrotation of the spinal motion segment in the transverse plane requiresforce application anterior to the axis of rotation. This forceapplication is possible with screws advanced through the pedicles from aposterior approach. However, this approach requires the transverseconnection element 4 and the freedom of rotational and translationalmovement of the fixation screw relative to the element 4, and of theelement 4 relative to the osteosynthesis rod 1.

In the past, the deformed spine has been translated to a rigidpre-contoured longitudinal implant. In another technique, apre-contoured longitudinal implant is engaged to the spine and then theimplant is rolled within the patient, ostensibly correcting the spinaldeformity. However, this technique of rolling the rod leading to torquetransference towards the ends of the instrumentation can be problematicand a contributor to spinal decompensation. Moreover, rolling the roddoes not control much rotation of the spine in the transverse plane, andmay actually increase torsion in the spine to contribute to an alreadyexisting rotational deformity through force applications actingposterior to the axis of rotation in the transverse plane. The presentinvention addresses these problems with prior art systems.

In particular, this invention recognizes that the vertebrae must be ableto angulate in the sagittal plane, as well as translate anteriorly orposteriorly in this plane. The vertebrae must likewise be able totranslate and rotate in the transverse plane, which plane ,is mostaffected by controlled torsion of the rod 1. Without this freedom ofmovement, that is with all the components rigidly fixed together, thespine will bind and will not correct segmentally when torsion is appliedto the rod. These principles are illustrated in FIGS. 11A and 11B. Aspinal rod 1 extends on one side of the spine and is engaged at its endsby way of bone screw assemblies 15 to vertebrae adjacent to thedisplaced vertebra. The construct includes a lateral connection element4, in which the ring 8 of the element is clamped to the rod 1. A boneanchorage element 3 is engaged through the pedicle and into the anteriorbody of the displaced vertebra. This anchorage element, or screw 3, isengaged to the arm 9 of the lateral connection element 4. This assemblyis identical to the assembly shown in FIG. 3.

As with the prior described assembly, the anchorage screw 3 is free totranslate and rotate along the arm 9. In this construct, a correctivetorsional force 35 is applied to the rod 1 so that the lateralconnection element 4 rotates in the direction of the arrow 36. As therod 1 is rotated, the arm 9 also pivots in the direction of arrow 37which causes the affected disk to move in the direction of arrow 38toward its proper position. The corrective force that moves the vertebraback to its position is applied through the arm 9 and through theanchorage screw 3 directly into the vertebra. Since this correction inthe transverse plane requires both rotation and translation of the axisof the motion segment, the anchorage screw 3 must be free to translatealong the arm 9. Thus, the screw 3 will translate in the direction ofthe arrow 39 toward the end of the arm 9 as the affected vertebraassumes its correct position relative to the adjacent vertebrae. Oncethe vertebra has been properly positioned in the transverse plane, theanchorage screw 3 is locked onto the arm 9 of the lateral connectionelement 4 to complete this aspect of the construct.

It should, or course, be understood that the screw assemblies 15 are notrigidly clamped to the rod 1, so that these assemblies operate as abearing for the torsional movement of the rod 1. One significant benefitof this approach is that unlike prior systems this direct derotationstill permits subsequent segmental sagittal plane angulation, which isnecessary to correct the motion segment in the sagittal plane. Thisdescribed approach for direct derotation produces a rotation/translationof the vertebra to be treated.

The lateral connection element 4 and the many degrees of freedomprovided by the system shown in FIGS. 11A and 11B permits greatflexibility in the application of corrective forces to the spine. Forinstance, the lateral connector element 4 can be free to rotate aroundthe rod, and the anchorage screw 3 free to rotate and translate alongthe arm 9 of the lateral connection element 4.

The tools to achieve the in situ contouring of the osteosynthesis rod 1are depicted in FIGS. 12-16. Bending irons of known design can be usedin some applications to contour the ductile rod in situ. However, it hasbeen found that since the bending of the rod occurs within the patientusing in situ contouring, the anatomical restrictions have dictated thedevelopment of new tools. For example, the L-bender shown in FIGS. 12Aand 12B are configured for corrections ill the frontal plane.Specifically, the L-bender 40 includes a long lever arm 41 that ismanipulated by the surgeon, a right angle beard 42 at one end of the arm41 leads to the gripper arm 43. At the terminal end of the gripper arm43 is a groove 44 defined therein to receive the osteosynthesis rod 1therein. As can be seen from FIG. 12A, the groove 44 is oriented at anangle relative to the plane of the lever arm 41, more particularlybecause the gripper arm 43 is itself angled upward at the right anglebend 42. Left and right L-benders are provided with the gripper arm 43and groove 44 oriented 90° opposite from that shown in FIGS. 12A-12B.Thus, the surgeon can place two L-benders immediately adjacent with thelever arms 41 diverging to provide room for the arms to be manipulatedto contour the ductile rod.

The L-bender 40 can also be used to facilitate alignment and connectionof the various implants as they are being inserted into the patient. Inusage, the fulcrum for the bending force applied to the rod is at thebase of the bender 40, that is at the right angle bend 42. With the longlever arm 41, significant but controlled forces can be applied to bendthe rod with less effort.

It has also been found that contouring rods at any time can causeindentations on the rod, which can ultimately lead to early fatigue orfracture. The rod grip bender 45 depicted in FIGS. 13A-13B addressesthis problem. The rod grip bender 45 includes a pair of jointed arms 46and 47, which terminate beyond the pivot joint in a pair of aperturehalves 48 and 49. The aperture halves 48 and 49 are configured toreceive and grip the osteosynthesis rod 1 therein when the arms 46 and47 are closed together. A locking mechanism 50 is provided at theopposite end of the arms 46 and 47 to lock the arms relative to eachother, and to thereby lock the rod grip bender to the rod to becontoured.

Two other tools useful in performing in situ contouring of the rod arethe traction rotator 52, shown in FIGS. 14A-B, and the counter-rotator65, shown in FIGS. 15A-B. The traction rotator 52 and counter-rotator 65are configured to engage a lateral connection element which is ofmodified design with respect to the connection element 4 describedabove. This modified lateral connection element 75, depicted in FIG. 16,is in many respects similar to the element 4. For example, the element75 includes an arm 76 radially extending from a ring 77. The ring 77 hasan aperture 78 sized to receive the spinal rod 1 therethrough. A numberof threaded apertures 79 are provided to receive set screws in the samemanner as the connection element 4 shown in FIG. 1. The primarymodification presented by the lateral connection element 75 is theprovision of a dimple 80 in the free end of the arm 76, and acorresponding oppositely located dimple 81 in the ring 77. The purposeof these dimples 80 and. 81 will be explained in connection with therotator 52 and counter-rotator 65.

The traction rotator 52 is configured to rotate the lateral connectionelement 75 relative to the rod 1, while also permitting traction of ananchorage screw such as a screw 3, relative to the arm 76 of the lateralconnector element. The traction rotator 52 includes a pair of arms 53and 54 pivotably mounted near the gripping end of the arms. As with therod grip bender 45, the arms include a locking mechanism 55 for lockingthe arms relative to each other.

The working end of the traction rotator 52 is configured to grip thering 77 of the lateral connection element 75 to allow it to be rotatedrelative to the rod 1. Thus, the terminal end of arm 54, namely end 56,may include a pair of arms 57 separated by a slot 58 to cradle oppositesides of the ring 77, or the head of the spinal screw mounted on the arm76. The other arm 53 terminates at its end 60 in a projection 61 whichis is adapted to extend into the dimple 81 formed in the ring 77. Thus,this traction rotator 52 provides means for engaging the ring 77 of thelateral connection element 75 so that it can be rotated relative to therod 1. Moreover, as seen in FIG. 14B, the ends 56 and 60 of the tractionrotator 52 are configured to extend around from one side of the rod tothe other to permit application of a traction force to the rod, even asthe rod is rotated. The tool 52 does not interfere with the free slidingmotion of the anchorage screw along arm 76 of the lateral connectionelement 75. Thus, where the correction requires rotation and translationof the vertebra to be treated, use of the traction rotator 52 permitsfree movement of the bone screw as the vertebra seeks its anatomicneutral position.

The counter-rotator 65 primarily operates as an anchor at one level whenthe traction rotator 52 is being manipulated at a higher level. Thecounter-rotator 65 includes a pair of arms 66 and 67 pivotably engagednear their respective ends. The arm 66 includes a working end 69 havinga recess 70 formed therein. This recess 70 is configured to receive thefree end of arm 76 of the lateral connection element 75. Opposite therecess 70, on the working end 72 of arm 67, is a projection 73, which issimilar to the projection 61 of the traction rotator 52. This projection73 is configured to engage the dimple 81 in the ring 77 of the lateralconnection element 75.

The manner in which the foregoing tools 52 and 65 are used is depictedin FIGS. 17-19. Each set of figures represents "before and after"representations of the motion segments as viewed from the frontal,sagittal and transverse planes. First, with reference to FIG. 17A, amodified traction rotator tool 85 is shown. This tool is the substantialequivalent of the tool 52 shown in FIGS. 14A-B in that it includeshinged arms 86 and 87, with the working end of arm 87 terminating in aprojection 88. The projection 88 is configured to be received within adimple 81 in the ring 77 of a lateral connection element 75. Thetraction rotator 85 is modified in that the working end of the secondarm 86 includes a barrel 89 formed at the end of the arm. The barrel 89is sized to receive the arm 76 of the lateral connection element 75.This barrel 89 is a substitute for the forked arms 57 of the rotator 52.As shown in FIG. 17A, the barrel 89 is slidably received over the freeend of the arm 76 of the lateral connection element 75. The barrel 89 isof sufficient depth to allow the barrel to move significantly along thelength of arm 76.

As shown in FIGS. 17-18, the instrumented vertebrae are labeled V₁ -V₃,with the middle vertebra V₂ being misaligned. The object, then, is toreorient the middle vertebra to bring it into alignment with thevertebrae V₁ and V₃. This object can be accomplished by orienting alongitudinal implant, such as rod 1, along the spine. A bone screwassembly 15 is engaged into each vertebra, as shown most clearly in FIG.18A. Each bone screw assembly 15 is connected to the rod 1 by way of apair of lateral connection elements 75 and 75'. In each pair, the ring77 of one element is threaded onto the rod 1, while the ring of theother element 75' is threaded onto the arm 76 of the first element. Thearm 76 of the second lateral connection element 75' extends generallyparallel to the principal rod 1.

In the illustrated procedure, a counter-rotator 65 is used to grip thelateral connection element 75 of the lowest vertebra V₃ in the mannerdescribed above. The bone screw assembly 15 at this level can be rigidlyfixed to its corresponding lateral connection element. However, thecomponents instrumenting the middle vertebra V₂ are engaged but remainloose so that the components can translate and rotate relative to eachother, in the manner described above in connection with the in situcontouring principles. The traction rotator 85 is then used to grip theends of the lateral connection element 75, with the barrel 89 slidingover the arm 76 until it contacts the second lateral connection element75' to which the bone screw assembly 15 is attached.

The correction is accomplished by holding the counter-rotator 65generally rigid, which thereby holds the vertebra V₃ and the rod 1generally immobile. Next, the traction rotator 85 is rotated in thedirection of the arrow 90 in FIGS. 17B, 18B and 19B, or away from thespinous process. The goal of this rotation is to manipulate thedisplaced vertebra V₂ back into its proper orientation. As the tractionrotator 85 is pivoted, the lateral connection element 75 that is engagedby the rotator also rotates about the rod 1. The second lateralconnection element 75' that supports the bone screw assembly 15 alsorotates about the arm 75 of the first connection element 75. Asdescribed above, the manipulated vertebra V₂ will automatically seek itsproper position, provided the fixation components are free to translateand rotate relative the fixation rod 1. The vertebra V₂ is rotatedbecause the rotation applied by the traction rotator 85 is translatedthrough the lateral connection elements 75 and 75', through the bonescrew assembly 15 and into the vertebra.

It can be appreciated that as the vertebra V₂ moves toward its alignedposition, the bone screw assembly 15 moves relatively laterally, closerto the rod 1. Thus, the second lateral connection element 75' willautomatically slide along the arm 76 of the first connection element 75in the direction of the arrow 91 in FIGS. 17B and 19B. The barrel 89 ofthe traction rotator 85 is maintained in contact with the second lateralconnection element 75' by squeezing the arms 86 and 87 of the tool 85together. Alternatively, translation of the element 75' along the arm 76can be forced by compressing the tool as it is rotated.

This direct derotation of the spine as thus far described contemplatesusing the traction rotator 85 with the barrel 89 engaged over the at,75. However, these same direct derotation principles call beaccomplished using the traction rotator 52 shown in FIGS. 14A-B. In thisinstance, the forked arms 57 would directly contact the ring of thesecond lateral connection element 75'. Since the ring of the secondelement 75' will slide along the arm 75 of the first connection element75, the arms 53 and 54 of the traction rotator 52 must naturally begradually closed together until the derotation is complete.

By comparing the sets of "before and after" figures, it can be seen thatthe vertebra V₂ translates laterally (FIG. 17B) and rotates (FIG. 19B).Moreover, the adjacent vertebrae V₁ and V₃ angulate in the sagittalplane, as represented by the diverging arrows 92, so that all of thevertebrae assume their proper anatomical orientation.

The traction rotators 52 and 85, and the counter-rotator 65 provideanother means for correcting spinal deformities by direct derotation ofthe vertebra to be treated. It is contemplated that this directderotation can be used in conjunction with in situ contouring to achievecomplete correction of deformities in all three planes and in all threespinal columns. A typical procedure may, for example, involve using therotators and counter-rotators to derotate one or more badly misalignedvertebrae. This direct derotation would then be followed by in situcontouring of the longitudinal implant to effect correction of theremaining deformities. Preferably, the direct derotation and in situcontouring will progress from the lowest level of instrumentation to thehighest. While the entire spine is being corrected, the presentinvention permits segmental correction, that is, correction limited toone motion segment at a time. This segmental procedure allows eachvertebra to seek its proper anatomic position without compromise andwithout closing the neural canal. It is anticipated that the sequentialsegmental correction may be repeated from bottom to top until the spineis nearly perfectly aligned.

In many instances, correction of a spinal deformity requires anchoringthe inferior end of the rod construct in the sacrum. Various systems forsacral fixation are known in the art, but do not contemplate a systemadapted for in situ contouring or that will significantly resist pulloutof the sacral screws. In another aspect of the invention, an intrasacralfixation construct is depicted in FIGS. 20A-B. This intrasacral fixationinvolves three concepts. In the first, an osteosynthesis rod 100 isimplanted along the spine in which the greatest portion 101 of the rodbears surface asperities, as on rod 1 described above. This portion 101is used for fixation to the upper vertebrae of the spine in a manner asset forth in the earlier described embodiments. The inferior end 102 ofthe rod can include the asperities, or can be smooth for insertion intoa bore 104 formed in the lateral sacral mass. In the preferredembodiment, this bore 104 is slightly curved, as shown in FIG. 20B.

The rod 100 is supported not only by the portion 102 engaged in thesacrum, but also by a sacral screw 105 that enters the superior portionof the sacrum at an angle, in the second concept of this inventivefeature. In the preferred embodiment, this screw 105 extends through thesubchondral bone of the sacrum and through the L5-S1 disc endplate, ascan be seen in FIG. 20A. The screw 105 includes an oblique canal 106 forreception of the rod 100 therethrough. The rod 100 is clamped within theoblique canal 106 by one or more set screws 107 or other lockingmechanism. The canal 106 may be oriented at a number of angles relativeto the axis of the screw 105 as dictated by the anatomy.

The head of the screw 105 is preferably buried into the bone to reducethe external profile of the implant and to orient the axis of the rod100 closer to the axis of rotation of the pelvis. To facilitate buryingthe screw into the bone, the screw 105 preferably includes a set screw107 projecting from the top of the screw head. The screw head alsopreferably includes a hex driving feature to receive a driving tool fromthe top. The screw 105 is then threaded into the sacrum from directlyabove and immediately adjacent the iliac crest. Once the screw is drivendeep into the bone, a channel is carved from the sacrum aligned with theoblique canal 106 in the screw 105. This channel will receive the spinalrod 100 when it is loaded into the sacral screw 105. One screw that iswell suited for use in this manner is a sacral screw provided bySOFAMOR, SA of Rang du Fliers, France, under part reference, number 9 6025.

A third feature of the intrasacral fixation resides in a "buttressing"effect provided by the ilium in the region of fixation. In particular,as shown in FIG. 20B, the ilium I overlaps a portion of the sacrum inwhich the rod 100 is mounted. Thus, the ilium I helps support the distalrod and protect the screw 100 in S1 from excessive stresses that lead toscrew pullout in prior systems. Moreover, the insertion of the endportion 102 of the rod 100 into the sacrum adds further resistance tomoments and stresses generated by corrective forces applied to the rod100 and vertebrae.

Moments and stresses are applied to the intrasacral fixation by the insitu contouring of the rod 100 when its distal end 102 is engaged in thesacrum. For example, in FIG. 20B rod benders 109 are shown applied tocontour the rod at the lumbosacral junction. Correction at this levelmay be necessary to address a severe scoliosis or correct an improperpelvic tilt. The sacral "buttress" effect provided by the ilium and thesacral engagement of the rod portion 102 resist the flexural bendingloads exerted while the rod is contoured. These same features arebeneficial once the instrumentation is complete to enlist the leverageprovided by the pelvis in reducing stresses to the sacral screws 105during the fixation. One further advantage is that the sacral screw 105can be placed in the S1 vertebra farther from the instrumentation in L5(not shown), augmented by the rod end portion 102 and the iliac"buttress".

A further application of the lateral connection element 4 describedabove is depicted in FIGS. 21A-21B. In particular, the lateralconnection element 4 provides means for engaging two vertebral fixationelements at the same level. In prior systems, vertebral fixationelements, such as hooks or screws, were mounted serially on the spinalrod. However, this serial approach is limited by the portions of thevertebra available for engaging a hook or screw. Other prior systemsprovide a lateral extension for supporting a second hook or screw in thesame vertebra, but this second screw is necessarily superior or inferiorto the first vertebral fixation element.

The present invention provides means for engaging more than one fixationelement into a given vertebra. For example, as shown in the leftconstruct in FIGS. 21A-B, a hook 110 is shown mounted to the rod 1 in amanner as depicted in FIG. 1. Immediately adjacent hook 110 is a lateralconnection element 4 of the type shown in FIG. 1. A second lateralconnection element 4' is engaged to the arm 9 of the first such element4. The arm 9' of this second element 4' extends parallel with the rod 1and back toward the level of the hook 110. A second vertebral fixationelement, such as hook 111, is then mounted to the second arm 9'.

Alternatively, a construct as shown in the right side of the figures canbe implemented using similar lateral connection elements 4. In thisconfiguration, the first hook 112 and second hook 113 are a nearly thesame level. In either case, the set of hooks can be manipulated toengage the same vertebra, or can engage adjacent vertebra fordistraction.

Moreover, one of the hooks of the pair can be replaced by a bone screw.For example, the hook 112 in the right construct can be replaced by abone screw, such as the screw assembly 15 in FIG. 3. The screw can beengaged in the pedicle and the hook 113 engaged to the lamina of thesame vertebra. The addition of the hook helps strengthen the constrictagainst pullout of the pedicle screw. Again, it is the versatility ofthe lateral connection element 4 that perslits fixation constructs notyet found in the art.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

What is claimed is:
 1. A spinal osteosynthesis device comprising:atleast one rod (1); at least two bone anchorage elements (3, 15)configured to be anchored to a vertebra; and at least one connectionelement (4) for connecting the rod (1) to at least one said boneanchorage elements, said connection element includinga ring (8) which isso dimensioned that the rod can be mounted therein to move freely inrotation and translation; means (14) for fixing the ring on said rod;and an elongated cylindrical arm (9) radially extending from said ringfor connection to said at least one bone anchorage element, said arm andsaid ring constituting a unit in one piece; wherein said at least onebone anchorage element (3) includes a U-shaped body (5) defining apassage (10) adapted to receive said cylindrical arm (9) extendedtherethrough permitting rotation and translation of said U-shaped bodyabout said arm.
 2. The spinal osteosynthesis device according to claim1, wherein said means for fixing includes at least one screw (14)extending through a radial aperture (13) in the ring (8) and bearingagainst the rod (1).
 3. The spinal osteosynthesis device according toclaim 1, wherein the ring (8) is open and defines a slot (20)therethrough to said passage (10).
 4. The spinal osteosynthesis deviceaccording to claim 1, wherein the surface of the arm (9) has a roughfinish (11).
 5. The device according to claim 4, wherein said roughfinish is obtained by knurling.
 6. The spinal osteosynthesis deviceaccording to claim 1, wherein said ring (8) is provided with a series ofapertures (13) arranged on its periphery in such manner that at leastone thereof is accessible to the surgeon for inserting a clamping screw(14) therein, regardless of the angular position of the ring on the rod.7. The spinal osteosynthesis device according to claim 1, wherein saidpassage (10) of the U-shaped body (5) of the anchorage element is closedby a screw threaded plug fixed to the anchorage element (3) afterinsertion of the elongated arm (9) of the connection element (4) intosaid passage, on which the plug acts radially for exerting a clampingforce.
 8. A spinal fixation system for correction of spinal deformities,comprising:a longitudinal member sized to extend between a plurality ofvertebrae along the length of the spinal column; a plurality of boneanchorage elements, each having a portion configured for engaging acorresponding one of the plurality of vertebrae, and each having aportion defining a passage therethrough; a lateral connection elementdisposed between at least one of said bone anchorage elements and saidlongitudinal member, said connection element includinga body havingmeans for slidably engaging said body to said longitudinal member sothat said body is free to move in rotation about and translation alongthe length of said longitudinal member without being disengagedtherefrom; and an elongated arm attached to said body and extendingoutward therefrom away from said longitudinal member when said body isengaged thereon, said arm configured to be received within said passageof said at least one bone anchorage element so that said at least onebone anchorage element is permitted to move freely in rotation andtranslation about said elongated arm; and means associated with each ofsaid plurality of bone anchorage elements for fixing said element on oneof said longitudinal member or said arm of said lateral connectionelement.
 9. The spinal fixation system of claim 8, wherein:saidlongitudinal member is an elongated rod; and said body of said lateralconnection element defines an opening therein sized to slidably receivesaid elongated rod therethrough.
 10. The spinal fixation system of claim9, wherein said body of said lateral connection element is a cylindricalring encircling said rod.
 11. The spinal fixation system of claim 8,wherein:said at least one bone anchorage element includes a U-shapedbody defining said passage for receiving said arm of said lateralconnection element therein; and said means for fixing associated withsaid at least one bone anchorage element includes a fixing elementinsertable in said U-shaped body of said anchorage element and having aopening therein for receiving said arm therethrough when said fixingelement is inserted in said U-shaped body.
 12. The spinal fixationsystem of claim 8, wherein said elongated arm and said body constitute aunit in one piece.
 13. The spinal fixation system of claim 8,wherein:said means for slidably engaging includes an opening sized toslidably receive said longitudinal member therethrough; and said meansfor fixing includes a screw extending through an aperture in said bodyintersecting said opening, said screw bearing against said longitudinalmember or said arm received within said opening in said body.
 14. Thespinal fixation system of claim 8, wherein said elongated rod iscylindrical and said opening in said body of said lateral connectionelement is circular.
 15. A method for correction of a spinal deformitycomprising the steps of:implanting a longitudinal member extendingbetween a plurality of vertebrae along a portion of the length of thedeformed spine of the patient; engaging at least one bone anchorageelement to each of the plurality of vertebrae; connecting each boneanchorage element to the longitudinal member; and manually bending thelongitudinal member within the patient with the vertebrae connectedthereto to thereby manipulate the vertebrae to correct the spinaldeformity by the bending of the rod.
 16. The method for correction of aspinal deformity of claim 15, wherein said step of connecting each boneanchorage element includes laterally offsetting at least one anchorageelement from the longitudinal member.
 17. The method for correction of aspinal deformity of claim 16, wherein said step of connectingincludes:connecting a connection element to the longitudinal member topermit relative rotation and translation between the connection elementand the longitudinal member; and connecting said at least one anchorageelement to said connection element laterally offset from saidlongitudinal member.
 18. The method for correction of a spinal deformityof claim 15 wherein said step of connecting each bone anchorage elementincludes connecting each element to permit relative rotation andtranslation between the element and the longitudinal member whilemaintaining the connection therebetween.
 19. The method for correctionof a spinal deformity of claim 18, further comprising:maintaining theconnection between each element and the longitudinal member during saidbending step while permitting relative rotation and translation; andthereafter fixing each element to the longitudinal member aftercorrection of the spinal deformity.
 20. The method for correction of aspinal deformity of claim 19, wherein said step of connectingincludes:connecting a connection element to the longitudinal member topermit relative rotation and translation between the connection elementand the longitudinal member; and connecting said at least one anchorageelement to said connection element laterally offset from saidlongitudinal member.
 21. The method for correction of a spinal deformityof claim 15 wherein the longitudinal member is a strong ductile rod. 22.The method for correction of a spinal deformity of claim 15, wherein thelongitudinal member is an elongated cylindrical rod.
 23. The method forcorrection of a spinal deformity of claim 15, furthercomprising:maintaining the connection between each element and thelongitudinal member during said bending step, while permitting relativerotation and translation between some of the elements and thelongitudinal member; and thereafter fixing each element to thelongitudinal member.
 24. The method for correction of a spinal deformityof claim 15, further comprising:fixing some of the bone anchorageelements relative to the longitudinal member prior to said bending step.25. A method for correction of a spinal deformity comprising the stepsof:implanting an elongated rod extending between a plurality ofvertebrae along a portion of the length of the deformed spine of thepatient; engaging a bone anchorage element to each of the plurality ofvertebrae; connecting an elongated connection element to the rod topermit rotation of the connection element relative to the rod;connecting one of the bone anchorage elements to the elongatedconnection element to permit translation of the anchorage elementrelative to the connection element; connecting the remainder of the boneanchorage elements to the elongated rod; holding the rod againstrotation; rotating the connection element relative to the rod whilepermitting the one bone anchorage element to slide along the connectionelement, to thereby manipulate the vertebra by the rotation of theconnection element to which the one bone anchorage element is engaged;and fixing all of the bone anchorage elements relative to the rod.
 26. Aspinal fixation system for correction of spinal deformities,comprising:an elongated member sized to extend between a plurality ofvertebrae along a portion of the length of the spinal column; a firstbone anchorage element having a body portion with means for mountingsaid body portion on said elongated rod, and a portion configured toengage one of the plurality of vertebrae; first and second connectionelements, each having a body defining an opening therethrough and an armintegral with said body and extending outward therefrom; and a secondbone anchorage element having a second body portion with means formounting said second body portion on said arm of said second connectionelement, and a second portion configured to engage said one of theplurality of vertebrae; wherein said first connection element is engagedto said elongated member with said member extending through said openingin said body of said first connection element, and said secondconnection element is engaged to said first connection element with saidarm of said first connection element extending through said opening insaid body of said second connection element.